1. Field of the Invention
The present invention relates to a substrate processing unit such as a coating and developing unit for performing a coating process and a developing process for a substrate such as a glass substrate. The present invention also relates to a conveying unit for use with such a substrate processing unit.
2. Description of the Related Art
In a unit that performs a coating process and a developing process for glass substrates used for liquid crystal displaying units (referred to as LCDS), the glass substrates are accommodated in a cubic or rectangular parallelopiped one-side opened accommodating cassette (referred to as carrier cassette) in such a manner that the glass substrates are horizontally arranged and kept in parallel. A conveying mechanism conveys a glass substrate from the carrier cassette to a coating unit or a developing unit.
FIG. 17 is a perspective view showing the relation between the conveying mechanism and the carrier cassette.
Referring to FIG. 17, a conveying mechanism 100 can be traveled in for example Y and Z directions and rotated in 2 direction. The traveling mechanism 100 has a pair of tweezers 101. The tweezers 101 can be traveled in X direction.
First, the conveying mechanism 100 is traveled. The conveying mechanism 100 is stopped in front of the carrier cassette C. The conveying mechanism 100 is traveled in Z direction so that the tweezers 101 are aligned to the height of a lower space of a relevant glass substrate G (see FIG. 17(1)). In this state, the tweezers 101 are inserted between the glass substrate G and a glass substrate G on the lower adjacent stage (see FIG. 17(2)).
Next, the tweezers 101 are upwardly traveled so as to pick up the glass substrate G (see FIG. 17(3)). The tweezers 101 that have picked up the glass substrate G are extracted from the carrier cassette C. Thus, the glass substrate G is extracted from the carrier cassette C (see FIG. 17(4)). The conveying mechanism 100 transfers the glass substrate G to a main arm (not shown) that conveys the glass substrate G to the next processing unit.
When such a coating and developing unit processes glass substrates G with different thickness, one carrier cassette accommodates glass substrates G with different thickness.
However, when the conveying mechanism 100 conveys glass substrates with different thickness to the carrier cassette C, the following problems may take place.
As a first problem, since the sizes of LCD glass substrates G are relatively large, the glass substrates G tend to flex. However, when the glass substrates G have different thickness, the flexure amounts thereof vary. Thus, corresponding to the thickness of the glass substrate G, the access position of the tweezers 101 should be designated. To do that, for example, a means that detects the thickness of each glass substrate G accommodated in the carrier cassette C is required.
As a second problem, before the unit is shipped, the tweezers 101 have been adjusted so that they are inserted into the center position of a space formed between two adjacent glass substrates G. However, when the unit is installed on site, the relation between the positions of the conveying mechanism 2 and the carrier cassette C deviates. Thus, after the unit has been installed, the access position should be corrected. However, when the glass substrates G have different thickness, the access position should be changed for each glass substrate G. Thus, the installing operation for the unit becomes complicated. In particular, since a conventional processing unit has a plurality of carrier cassettes C, the access position should be adjusted for each carrier cassette C and for each glass substrate G that has different thickness. Thus, the installing operation for the unit becomes complicated.
In addition, when one carrier cassette C accommodates glass substrates G with different thickness or when a carrier cassette C accommodating glass substrates C with different thickness is conveyed from the outside to the unit, the conveying position or the processing conditions of each processing portion in the unit should be changed. Since it takes a long maintenance time to change the access position, the yield of the unit deteriorates. In addition, if a processing condition is incorrectly set, a glass substrate G may collide with the casing of the unit or a carrier cassette C. Thus, the carrier cassette C may be damaged. Consequently, the yield of the unit deteriorates. If a processing condition in the processing portion is incorrectly set, due to the incorrect processing condition, the yield of the unit deteriorates.